BrianRMV

I'm beginning to thing that retarded timing, limited performance, and poor fuel economy all point to the same culprit. My list of items that might be responsible are:
- Knock sensor. This has been replaced, but maybe the harness is bad.
- Speed and/or reference sensor. I don't know exactly what either of these do to timing, but believe one or both have connectivity issues. I have a fairly regular "no start" that is resolved by wiggling the harness connections near the fire wall.
- Hall sensor. I just read about this on a few threads. Is it just another name for the speed or reference sensor?
- DME faulty?
- KLR faulty?

Anything you would add to the list?

Perry 951

Did you ever check into the items I've suggested?

BrianRMV

I checked the FQS position a while back. Honestly, I was not 100% certain I was getting positive bite on the adjustment, and was reluctant to force it, so this is potentially something to double check. I have asked the mechanic currently working on it to check the position.

The blink codes were checked a while back. I had a 3-3 and another code. I may have trouble finding the codes, but as I recall, the combination of the two codes said to ignore them. Again, this is something I need to re-check.

The cat has been removed. For a while I was convinced I had a collapsed crossover pipe. That was a painful financial experience. I now have a spare crossover pipe if anyone is in need.

Perry 951

Any code set is not something to ignore. Although these systems are simply antiquated in comparison to today's ECU's, they are smart enough to tell you some general areas to check.
Here's a link to the OEM service manual section for codes and what to test when they set. https://members.rennlist.com/951_rac...BlinkCodes.pdf

Code 3-3
Pressure sensor in K/CP control unit defective
Note - Flashing code 3 - 3 may be caused by a detective throttle valve potentiometer. Therefore, first check the throttle valve potentiometer in accordance with Item 9 (code 4-1) before replacing the control unit.

Code 4-1
Throttle potentiometer Plug connector has fallen off; supply line to potentiometer has ground contact; potentiometer is defective.
Note - If defect signal 3 - 3 is present at the same time, the pressure sensor is in good condition.

BrianRMV

Thanks for the input Perry. I'm almost certain that the blink codes were 3-3 and 4-1. I think I can confirm that with the mechanic who did the blink code test. The TPS has been replaced and I have confirmed that it was adjusted properly. I have wondered if the harness could be faulty. I have heard that wiring near the connector or the connector itself frequently fail. I performed the Clark's Garage test on it and it was within spec, but maybe under driving conditions it fails. Also, I believe that it has be removed and reinstalled after I ran the test, so the wires and/or connector could have been damaged in the process.

Perry 951

I'd inspect the pigtail end of the TPS sensor or just replace it since it tossed the 4-1 and you have a new sensor. The harnesses get very brittle in that area because of the heat from the turbo and the 90 degree turn of the TPS harness. An intermittent break would not be out of the question.

It would also be wise to check the pressure line to the KLR for leaks. A smoke tester works good for that.

Tom M'Guinn

I suspect you have multiple issues going on, including vacuum leaks, one or more sensor/harness issues, a clearly bad speed/ref sensor connector, and perhaps some A-tune issues.

I think your focus on ignition timing is throwing you or your mechanic off the scent. But to answer your question, the speed and ref sensors don't affect the timing per se -- they either work and enable the DME/KLR to produce the desired spark curve, or they don't work. When your car is not starting, their signals are not getting to the DME, almost certainly due to frayed wires in the harness. There isn't a separate/different Hall sensor as part of the engine management on these cars. I'd fix the speed/ref harness before doing anything else. Peel back the rubber boots on the harness. If they are frayed on the sensor side, just get new sensors. If they are frayed on the harness side, this will fix it:

https://www.lindseyracing.com/LR/Porsche/LR-944-HAR-REF.html

I'd also address all blink codes, smoke check for vacuum leaks, check the TPS, DME temp sensor, and knock signals at the DME/KLR connector (to test the harness and sensors), and revert to a stock chips for testing. There have been some threads in the past on idle issues with m-tune, so worth ruling out the a-tune, particularly since some of your issues started with its installation -- easy enough to eliminate that as a potential cause.

Then maybe update the thread with a complete list of remaining symptoms, and what's been tested and how, and maybe it will help pinpoint where to look if it's still acting up.

BrianRMV

Thanks for the input. As soon as I have anything to report I will update the thread.

BrianRMV

One thing that is really bugging me right now is not having an easy way to test the A-Tune. I don't think the A-Tune is defective, but maybe the installation was not done properly. It would be helpful to rule it out as a potential problem. When I added it, my dme needed to be modified from a 24 to a 28 pin setup. The pin modification was done by Dave Lindsey, so I'm sure it was done correctly. I would like to try the stock chip, just to see if there is any difference, but right now I'm stuck. I'd also like to try a known working dme and klr, but don't have access to one. It would probably be too much of a nuisance to operate, but it would be really nice if there was a parts exchange of some sort that would allow you to borrow known functioning parts.